Process and apparatus for densifying powder metal compact to form a gear having a hub portion,and preferred powder metal compact shape for use therewith

ABSTRACT

A process and apparatus are described for densifying a hot powder metal compact in incremental stages with a single stroke of a forming or forging press. Flow of metal during densification and deformation of the hot compact are controlled to prevent undesired flow of material between a hub portion and a main body portion of the final product to be produced. A preferred shape of powder metal compact is described for use with the process and apparatus disclosed herein.

Matted States Patent 1191 [111 3,8A2,646 Kuhn. 1 Oct. 22, 1974 [54]PROCESS AND APPARATUS FOR 3,605,518 9/1971 Haller 29 1592 DENSIFYINGPOWDER METAL COMPACT 3,731,516 5/1973 Dohmann et a1. 72/354 TO FORM AGEAR HAVNG A HUB PORTION, AND PREFERRED POWDER METAL COMPACT SHAPE FORUSE THEREWITH Howard A. Kuhn, Ardmore, Pa.

The Gleason Works, Rochester, NY.

Filed: Apr. 20, 1973 Appl. No.: 353,044

Inventor:

Assignee:

US. Cl 72/354, 72/359, 29/1592,

References Cited UNITED STATES PATENTS 10/1966 Haller 29/4205 FOREIGNPATENTS OR APPLICATIONS 1,190,150 4/1970 Great Britain 29/1592 PrimaryExaminer-Lowell A. Larson Attorney, Agent, or FirmRalph E. Harper 5 7]ABSTRACT A process and apparatus are described for densifying a hotpowder metal compact in incremental stages with a single stroke of aforming or forging press. Flow of metal during densification anddeformation of the hot compact are controlled to prevent undesired flowof material between a hub portion and a main body portion of the finalproduct to be produced. A preferred shape of powder metal compact isdescribed for use with the process and apparatus disclosed herein.

12 Claims, 5 Drawing Figures PROCESS AND APPARATUS FOR DENSIFYING POWDERMETAL COMPACT TO FORM A GEAR HAVNG A HUB PORTION, AND PREFERRED POWDERMETAL COMPACT SHAPE FOR USE THEREWITH "BACKGROUND AND BRIEF DESCRIPTIONOF INVENTION This invention relates to improvements in the final formingof metal products having (a) a main body portion, (b) a hub portionformed integrally with the main body portion, and (c) a bore extendingthrough the main body and hub portions. More specifically, the inventionis concerned with a process and apparatus for producing high strengthgear products from hot powder metal compacts, for use as side gears inpresent day automobile differentials.

It is known in the powder metal art to form ferrous metal products froma powder metal compact which has been heat treated and forged with knownforging equipment. Typically, a cold metal powder is compacted into apreferred shape and coherent form which can be more easily handledduring subsequent heating and forming operations. The powder metal canbe compacted with a known mechanical or isostatic pressing means whichimparts the preferred shape to the compact and which increases thedensity of the material making up the compact to approximately 75 to 90%of its theoretical value. Then the compact ,is sintered in a furnace toproduce a metallurgically clean compact having improved characteristicsfor placement in a die cavity of a forge or other forming means. Finalforming of the compact imparts a final shape to and increases thedensity of the final product to about 100% of its theoretical value. V

In the production of high strength ferrous metal parts, it is preferredthat certain compacting'and heat treating processes be applied to theferrous powder prior to forging, but these preliminary processes do notform a separate partof the present invention.

Certain shapes and forms of gear pieces present greater problems thanothers for final forming of a high strength, high density product. Thepresent invention is concerned with a type of gear piece which includes,for example, a hub portion formed integrally with a main body portionand which further includes a splined bore extending through the hub andmain body portions. The main body portion is shaped to include beveltooth profiles on one face thereof. A typical application for a gearpiece of this type is in an automobile drive train differential. Thisshape of product is difficult to form because known forming processesproduce an undesired degree of material flow between the hub and mainbody portions of the final product. For example, it would be possible toproduce such a part from a relatively long cylindrical compact which isgrossly deformed to radially expand one end thereof to form an enlargedmain body portion at the end of a cylindrical hub. However, this degreeof radial expansion is far in excess of strains which can be toleratedby certain ferrous materials, and fracturing of the final product islikely. Another method of forming a hub on a main body portion of a gearpiece would require backextrusion of the hub from a disc-shaped compact.This would require relatively complex equipment and extreme movements ofmaterial to produce the final shape, resulting in a low quality productand excessive wear of a die in which the product is shaped.

In contrast to the processes discussed above, the present inventioninvolves a process which starts with a compact shape having partiallyformed hub and main body portions with a bore extending therethrough.Final forming or forging of the compact is accomplished through steps ofincremental forming which sequentially densify and shape and hub portionand the main body portion of the compact, and the sequentialdensification and shaping are used to control material flow between thehub and main body portions so that gross displacements of material willnot occur.

The apparatus of the invention provides for rapid densification anddeforming of hot powder metal compacts into final, high strengthproducts with a single stroke of a forming press. During the singlestroke of the forming press, a compound forming tool, comprising a punchhaving first and second elements for contacting different parts of thehot compact, is brought into sequential engagement with the hub and mainbody portions of the compact. A first punch element makes contact withthe partially formed hub portion of the hot compact so as to press thehot compact onto a core rod support in a closed-end die cavity. The corerod support is provided with a splined configuration on its surface sothat splines are formed radially into the bore surface of the hotcompact as it is advanced into the die cavity. The first punch elementfunctions to densify and shape the hub portion of the compact withoutsignificant movement of material between the hub portion and the mainbody portion of the compact. The second punch element functions todensify and deform the main body portion of the hot compact after thehub portion has been densified by the first punch element. Sequencingmeans are provided for delaying the action of the second punch elementuntil the hot compact makes contact with the closed end portion of thedie and full densification of the hub portion is substantiallycompleted.

A preferred embodiment of the invention provides for a concentricmounting of the first and second punch elements, and each punch elementis positioned and mounted to be reciprocated back and forth in thedirection of the central longitudinal axis of a compact being formed.Both punch elements are mounted in a common ram or other driving meansand are simultaneously driven, in a forming stroke, toward the closedend of a die so as to engage and move a hot compact into the die cavity.The second punch element is resiliently mounted, in the axial direction,relative to the first punch element, and this provides for a sequentialtiming of the two punch elements in their respective contacts with thehub and main body portions of the hot compact. In this way, each punchelement applies an axial force to a separate portion of the hot compact,and the direction of movement of the axial forces corresponds to thedirection of movement of the ram or driving means during a formingstroke of the apparatus. Thus, each forming stroke of the ram impartsincremental steps of forming to a hot compact contained within afixed-position die cavity.

A preferred shape for a powder metal compact considers the shape of theclosed end portion of the die cavity into which the compact isintroduced and formed. In the case of a side gear pinion, of the type tobe described in this specification, the main body portion of the compactshould be provided with a generally curved face for contacting the angledefined by projecting tooth shapes formed in the closed end of the diecavity. This relationship avoids unwanted movements or stresses of themain body portion of the compact during densification of the compact.

These and other features and advantages of the present invention willbecome apparent in the more detailed discussion which follows. In thatdiscussion reference will be made to the accompanying drawings asbriefly described below.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an elevational view in sectionof a preferred shape of a powder metal compact for use with the processand apparatus of the present invention;

FIG. 2 illustrates an initial step of incremental forming of the compactof FIG. 1;

FIG. 3 illustrates a further step of incremental forming of the compactof FIG. 2;

FIG. 4 is an elevational view, in section, of a relatively simple formof apparatus for carrying out the process of the invention, showing theapparatus in a condition for applying a forming force to a hub portionof a compact contained within a die; and

FIG. 5 illustrates the apparatus of FIG. 4 in a condition for applying aforming force to a main body portion of a compact contained within adie.

DETAILED DESCRIPTION OF INVENTION FIGS. 1-3 depict various stages of theprocess of the present invention wherein a hot powder metal compact ofthe type shown in FIG. 1 is densified and formed to produce the finalgear product illustrated in FIG. 3. In each of the views the compact andfinal gear product are shown as including a main body portion 10, a hubportion 12 formed integrally with the main body portion, and a bore 14extending through the main body and hub portion. The bore 14 has asmooth surface in the initial compact form of FIG. 1 and is shown asincluding a splined surface in the views of FIGS. 2 and 3 aftersubsequent forming steps of the process have been applied thereto.Although this invention will be described in terms of producing thespecific gear form illustrated in FIG. 3, it can be appreciated that theprinciples of the invention generally apply to the manufacture ofproducts having a main body portion 10, a hub portion 12, and bore 14extending through the main body and hub portions.

In order to produce the specific gear form illustrated in FIG. 3, it ispreferred that the initial shape of a hot powder metal compact for usein the process of this invention be of the general form illustrated inFIG. 1. This compact form can be considered as a stepped shape or one inwhich there is a partially formed hub portion 12 and a partially formedmain body portion 10, both of which are to be further densified andshaped to establish the final product of FIG. 3. The weight distributionof powder between the hub and main body portions is substantially thesame as in the final part to be formed. The preferred compact shapeincludes a front face portion 18 for being received into a die cavity ofa forming apparatus. The front face portion is of a generallyhemi-spherical or curved shape for making progressive contact shape withangular projections of tooth profiles in the die cavity. The end portion16 of the compact is intended to be received against a flat closed-endportion of a die cavity, and an optional counterbore 19 may be includedin the end portion 16 to receive an ejector member. The relationshipbetween the shape of the compact and the die cavity into which it isplaced will be discussed in greater detail later with reference to FIGS.4 and S.

The basic concept of the process of this invention is one of applyingincremental axial forces to the compact of FIG. 1 to sequentiallydensify and shape the hub portion 12 and the main body portion 10 of thecompact. The forces which are applied to the separate parts of thecompact move in sequence in a common direction in such a way that thereis no substantial movement of material of the compact between the huband main body portions. This prevents the establishment of unwantedstresses between the hub and main body portions of the final product,and the entire process is carried out without gross movements or reversemovements of material relative to the direction of travel of toolingwhich imparts the axial forces to the hot compact.

FIG. 1 illustrates an initial step in the process wherein an axial forceis applied only to a terminal end face 20 of the hub portion 12 of a hotcompact which has been placed in a die cavity for a forging or formingoperation. The arrows shown in FIG. 1 depict the direction of the axialforce which is applied to the hub portion of the compact. This axialforce serves to initially densify the hub portion of the compact priorto any significant densification of the main body portion of thecompact. During the initial step of densifying the hub portion 12 of thecompact, a back face 22 of the main body portion of the compact isconstrained from moving toward or away from the hub portion 12. Thisresults in a substantial densification of the material contained in thepartially formed hub portion 12 of the compact illustrated in FIG. 1without any significant movement of that material into the main bodyportion of the compact.

After the hub portion has been substantially formed, as illustrated inFIG. 2, continued application of the initial axial force to the end face20, accompanied by an application of an axial force to the back face 22,results in a flow of material from the main body portion of the compacttoward the radially outward areas of the die cavity. This flow isillustrated by arrows in FIG. 2. This radial flow of material in themain body of the compact is initiated by a separate step of the processwhich applies a separate axial force to the back face 22 of the compact.The separate axial force moves in the same direction as did the firstaxial force which was applied to the hub portion of the compact, andthis provides for full densification and shaping of the main bodyportion of the compact. Since the hub portion 10 is essentially fullydensified and completed before forming of the main body portion isinitiated, there is little tendency for the material of the main bodyportion to reverse its flow in the direction of the hub portion. Thus,the hub and main body portions are sequentially densified and formedwith complete control of material movement during the incremental stepsof forming each portion.

The splined configuration which is imparted to the bore 14 of the hotcompact is imparted thereto simultaneously with the initiation offorming of the hub portion of the compact. In fact, the initial step ofapplying an axial force to the end face 20 of the compact illustrated inFIG. I can function to press the hot compact into supported engagementwith a core rod means having a splined surface so as to radially densifyand form a splined surface in the bore 14 of the hot compact. It isespecially advantageous to produce the splined configuration on theinner bore 14 during initial insertion of the hot compact into a diecavity because a more complete and precise configuration can be impartedto the bore while the compact is at its highest temperature in itsdelivery to the forming apparatus. Relatively high pressure is requiredto radially densify and shape the bore of a compact, and prior artmethods which have attempted this forming step at a later stage in thedevelopment of a gear shape have resulted in incomplete or inaccuratespline formations.

A simplified form of apparatus is depicted in the illustrations of FIGS.4 and 5 to illustrate a basic apparatus for carrying out the process ofthe present invention. Of course, it is to be understood that apparatusdesigned for a high speed production system would be relatively morecomplex and would include structures for automatically handling a hotcompact and the finished part in its movement into and out of a diecavity.

As shown in FIGS. 4 and 5 the apparatus is of a type which includes adie 30 having a cavity defined therein for imparting a final shape tothe compact being densified. Further, the apparatus includes a core rodmeans 32 which is supportedand contained-within the die 30 for beingreceived in the bore 14 of a compact which is inserted into the diecavity. The core rod means 32 is provided with a splined configurationfor a major length of its outside surface, and a reduced diameter endportion 33 may be provided for initially positioning a compact on thecore rod means prior to forging. The

apparatus may also include a known ejector mechanism 34 which comprisesa tubular member splined to the outside surface of the core rod means 32for closing off the end of the die cavity and for ejecting a finalformedproduct from the cavity by a movement upwardly along the length of thecore rod means 32. In the type of'apparatus illustrated, the position ofthe die 30 is fixed, and a separate punch means 36 is moved relative tothe die means to close the open end of the die means and to apply animpact to a compact contained therein. Apparatus of the type justdescribed is generally known in the art. The improvement of the presentinvention is concerned with the punch means 36 and the manner in whichit applies an impact force to a hot compact contained within the diecavity of the apparatus. In this regard, it is known to utilize acompound pressing tool, made up of separate punch elements, forinitially compacting a powder to produce a stepped compact shape of thetype shown in FIG. 1. However, the improved punch means of thisinvention comprises a compound tool having certain structures andfunctions which are different from those used in the art of pressingpowder into compact forms.

The improved punch is illustrated in FIGS. 4 and 5 as including a firstpunch element 38 and a second punch element 40. The first punch elementfunctions to apply an axial force to a partially formed hub portion of ahot compact after the hot compact is received on a core rod means 32, asshown in FIG. 4. The second punch element functions to apply a separateaxial force to a partially formed main body portion of a hot compactafter full densification of the hub portion is substantially completedso as to prevent significant material flow between the hub portion andthe main body portion. The functional application of the second punchelement is illustrated in FIG. 5. The two punch elements 38 and 40comprise tubular elements which are concentrically mounted relative toeach other so as to define, in combination, a closed end for the diecavity when the punch is inserted into the die. Both punch elements aremounted in a common ram or other driving means and are simultaneouslydriven back and forth in the direction of the central longitudinal axisof the compact being formed. During a forming stroke, both punchelements are moved in sequence towards the closed end (the bottom end inthe orientation of FIGS. 4 and 5) of the die cavity, and incrementalforming of the hot compact contained within the die cavity is achievedwith each full forming stroke. Thus, it is not necessary to subject thecompact to separate forming strokes in order to achieve the type ofincremental forming which is preferred by the present invention.

As shown in FIG. 4, the first punch element 38 includes an end face 44which substantially matches the terminal end face 20 (see FIG. 1) of thepowder metal compact being formed. In addition, the inner surface of abore portion 46 of the first punch member 38 includes a splinedconfiguration which mates with the splined configuration of the core rodmeans 32 to prevent extrusion of powder metal material between the firstpunch element and the core rod means.

The second punch element 40 is resiliently mounted, in the axialdirection, relative to the first punch element. In the relatively simpleapparatus depicted in FIGS. 4 and 5, spring means 48 are compressivelyloaded between the second punch element 40 and a portion of the ram 42which fixes the position of the first punch element 38 to thereby allowa limited distance of movement between the two punch elements. Thedistance of movement is set to correspond to the length of traveldesired for the first punch element 38 from the time it makes initialcontact with the hot compact to the time it is required that the secondpunch element 40 begin its densification of the main body portion of thehot compact.

Operation of the apparatus illustrated in FIGS. 4 and 5 involves aplacement of a hot compact on the free end of the core rod means 32.Then, the forming stroke of the apparatus is initiated by movement ofthe ram 42 downwardly so as to insert the free ends of the first andsecond punch elements into the open end of the die cavity. The free endsof the first and second punch elements are axially offset from oneanother so that both free ends make simultaneous contact with respectiveportions of the hot compact. During the insertion movement of the punchmeans 36 into the die cavity, the hot compact is pressed into supportedengagement with the core rod means and fully inserted into the diecavity until contact is made with closed end structures of the diecavity. During this insertion, spline configurations are formed in theinner bore of the hot compact. Continued movement of the punch means 36results in an application of an axial force to the hub portion of thecompact as a result of a continued advancement of the first punchelement 38 towards the closed end of the die cavity. At the same time,there is no axial movement of the second punch element 40, and thespring elements 48 are further compressed until a back end 50 of thesecond punch element 40 engages a surface 52 of the ram 42. Duringinitial densification of the hub portion of the hot compact, the secondpunch element 40 functions to confine the material of the hot compact toprevent unwanted movement from the hub portion to the main body portionthereof and to prevent radial outward movement of the hub portion. Afterthe hub portion of the compact has been substantially fully formed, thesecond punch element 40 initiates its axial movement against the backsurface 22 (see FIG. I) of the compact. This applies an axial force inthe main body portion of the compact, and moves material within the mainbody portion to a conforming contact with all exposed portions of thedie. Completion of the forming stroke is depicted in FIG. wherein thefinal product of FIG. 3 has been fully formed. It can be seen that anannular end face 54 of the second punch element 40 defines the back faceof the completed gear piece. Upon completion of the forming stroke, theram 42 is reciprocated in the opposite direction from the formingstroke, and all parts of the punch means 36 are withdrawn from the diecavity. After this, the ejector means 34 can be actuated to lift thecompleted gear piece out of engagement with the die.

Referring back to the relationships shown in FIG. 4, it can be seen thatthe curved face portion 18 of the compact, as discussed above withreference to FIG. 1, is shaped to progressively engage the angle definedby a plurality of tooth-shaped projections 56 which extend into the diecavity from the closed end thereof to define a series of tooth sidewallsand bottomlands for a gear. This relationship between the initial shapeof a forward end of the compact and the portion of a die which itcontacts is very important because a substantial mismatch between theshape of the compact and the shape of the die will produce a stress orbending moment in the compact as it is pressed rapidly into fullengagement with the die. This is especially true where the initialdiameter of the hot compact is substantially less than the full diameterof the die, thereby leaving considerable space for unwanted movements ofthe compact before controlled densification and forming have takenplace. In addition, it has been found that a tangential engagement ofthe tooth-shaped projections 56 with a curved surface of a compact ispreferred to a matching" engagement between such projections and acompact having a tapered face without a curved shape. This has theeffect of reducing tensile circumferential strains in the tips of theteeth being formed while increasing local compressive strains (axially)in each tooth. Also, it has been found that an increase in diameter ofthe main body portion of the compact has a similar desirable effect toincreasing the compressive strain along the length of the teeth (whichin turn increases the tolerable tensile strain transverse to the toothbefore cracking).

Having described a specific application of the present invention to atype of gear piece and present day usage, it can be appreciated that theprinciples of the invention can be applied to other productconfigurations in which it is desired to control stresses and materialdensity between body portions having substantially different sizes andshapes. Also, it can be appreciated that other designs of apparatus maybe used for practising the process of this invention. For example,separate punch elements may be separately controlled with separatemechanical drive elements, if desired. Additional applications of theprinciples of this invention to usages which would be contemplated bythose skilled in this art, in view of the teachings herein, are intendedto be included within the scope of the claims which follow.

What is claimed is:

1. A process for densifying a powder metal compact so as to form aproduct having (a) a main body portion, (b) a hub portion formedintegrally with the main body portion, and (c) a bore extending throughthe main body and hub portions, said process comprising the steps of:

placing the compact in a die cavity so as to be supported by a core rodmeans carried in said die cavity.

applying an axial force to a partially formed hub portion of saidcompact so as to press the compact against a closed end portion of thedie cavity and to fully densify the hub portion of the compact prior tofull densification of the main body portion of the compact, and

applying a separate axial force to a partially formed main body portionof said compact after full densification of said hub portion issubstantially completed so as to prevent significant material flowbetween the hub portion and the main body portion.

2. The process of claim 1 wherein said axial forces are sequentiallyapplied to said compact in a single stroke of a forming punch.

3. The process of claim 1 wherein said step of placing includes a stepof pressing said compact into supported engagement with said core rodmeans so as to radially densify an inner surface defining the bore ofthe compact.

4. The process of claim 3 wherein said step of pressing of the compactinto engagement with the core rod means forms a spline in the boresurface of the compact.

5. Apparatus for densifying a powder metal compact having (a) apartially formed hub portion, (b) a partially formed main body portion,and (c) a bore extending through the main body and hub portions, saidapparatus being of a type which includes a die having a cavity definedtherein for imparting a final shape to the compact being densified, acore rod means contained within said die for being received in the boreof the compact and for supporting the compact, and a punch means forapplying axial forces to the compact contained within said die, theimprovement in said punch means comprising a first punch element forapplying a first axial force to the partially formed hub portion of acompact after the compact is received on said core rod means, said firstpunch element being positioned to reciprocate in the direction of thecentral longitudinal axis of the compact so as to apply said first axialforce in a direction which presses the compact against a closed endportion of said die cavity to thereby fully densify the hub portion ofthe compact prior to full densification of the main body portion of thecompact,

a second punch element for applying a second axial force to thepartially formed main body portion of the compact after fulldensification of said hub portion is substantially completed so as toprevent significant material flow between the hub portion and the mainbody portion, said second punch element being positioned to reciprocatein the same direc- 9 tion as said first punch element so as to applysaid second axial force in a direction which presses the compact intoconforming contact with all parts of said die, driving means foradvancing said first and second punch elements toward said die to applysaid axial forces to a compact contained therein, and

sequencing means for delaying the application of said second axial forceby said second punch element until full densification of said hubportion is substantially completed.

6. The apparatus of claim wherein said first punch element includes atubular member having an end face which substantially matches a terminalend face of the hub portion of said powder metal compact.

7. The apparatus of claim 6 wherein said second punch element comprisesa tubular element positioned concentrically around said first punchelement and wherein said second punch element has an end face whichdefines a back face of the main body portion of the final product to beproduced.

8. The apparatus of claim 5 wherein said core rod means is provided witha spline configuration on its outer surface so as to form a splineconfiguration along the bore of said compact as the compact is pressedinto position of said core rod means.

9. The apparatus of claim 8 wherein said first punch element includes aspline configuration on a surface which mates with the outer surface ofsaid core rod means.

10. The apparatus of claim 7 wherein said first and second punchelements are mounted in a common ram structure driven by said drivingmeans so that both of said punch elements are moved together toward saiddie with each forming stroke of the ram structure, and wherein saidsecond punch element is resiliently mounted relative to said first punchelement so that said second punch element is delayed in its forwardmovement, upon engaging a portion of said compact, until said firstpunch element has advanced for a sufficient distance to substantiallycompletely densify the hub portion of the compact.

11. The apparatus of claim 5 wherein said die cavity has a configurationwhich establishes gear tooth profiles on a compact densified therein.

12. The apparatus of claim 5 wherein said powder metal compact has ashape which allows full insertion of the compact into said die cavity bythe action of said first punch element and without a bending momentbeing applied to the main portion of the compact relative to its hubportion.

UNITED sTATEs PATENT OFFICE CERTIFICATE OF CORRECTION 2am..- m.- ,6Dated. Oct. 22, 1974 Inventars) Howard A uhn It is certified thaterrorappears in the above-identified patent am! that said Letters Patent arehereby corrected as shownbelow:

v Column 2, "li he 9, change "and shape and" to 'v-and shape the-.

' Signed and seated this 24th day'pf Dee-ember 1974.-

(SEAL)-. Attest:

mcco'z 2-1. GIBSON JR. c. MARSHALL DANN Attest'i'ng Officer Commissionerof. Patents,

UNITED sTATEs PATENT OFFICE- CERTIFICATE OECORRECTION Regent No.3,842,646 v Dated Oct. 22; 1974 Howard A. Kuhn Inventcfls) It iscertified thaterror appears in the above-identified patent am! that saidLetters Patent are hereby corrected as shownbelow:

Column 2, line 9, change "and shape and" to-'-.-and shape the.

Signed and sealed this 24th daypf December 1974.-

(SEAL),- Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Attest'ing Officer Commissioner of.Patents,

1. A process for densifying a powder metal compact so as to form aproduct having (a) a main body portion, (b) a hub portion formedintegrally with the main body portion, and (c) a bore extending throughthe main body and hub portions, said process comprising the steps of:placing the compact in a die cavity so as to be supported by a core rodmeans carried in said die cavity, applying an axial force to a partiallyformed hub portion of said compact so as to press the compact against aclosed end portion of the die cavity and to fully densify the hubportion of the compact prior to full densification of the main bodyportion of the compact, and applying a separate axial force to apartially formed main body portion of said compact after fulldensification of said hub portion is substantially completed so as toprevent significant material flow between the hub portion and the mainbody portion.
 2. The process of claim 1 wherein said axial forces aresequentially applied to said compact in a single stroke of a formingpunch.
 3. The process of claim 1 wherein said step of placing includes astep of pressing said compact into supported engagement with said corerod means so as to radially densify an inner surface defining the boreof the compact.
 4. The process of claim 3 wherein said step of pressingof the compact into engagement with the core rod means forms a spline inthe bore surface of the compact.
 5. Apparatus for densifying a powdermetal compact having (a) a partially formed hub portion, (b) a partiallyformed main body portion, and (c) a bore extending through the main bodyand hub portions, said apparatus being of a type which includes a diehaving a cavity defined therein for imparting a final shape to thecompact being densified, a core rod means contained within said die forbeing received in the bore of the compact and for supporting thecompact, and a punch means for applying axial forces to the compactcontained within said die, the improvement in said punch meanscomprising a first punch element for applying a first axial force to thepartially formed hub portion of a compact after the compact is receivedon said core rod means, said first punch element being positioned toreciprocate in the direction of the central longitudinal axis of thecompact so as to apply said first axial force in a direction whichpresses the compact against a closed end portion of said die cavity tothereby fully densify the hub portion of the compact prior to fulldensification of the main body portion of the compact, a second punchelement for applying a second axial force to the partially formed mainbody portion of the compact after full densification of said hub portionis substantially completed so as to prevent significant material flowbetween the hub portion and the main body portion, said second punchelement being positioned to reciprocate in the same direction as saidfirst punch element so as to apply said second axial force in adirection which presses the compact into conforming contact with allparts of said die, driving means for advancing said first and secondpunch elements toward said die to apply said axial forces to a compactcontained therein, and sequencing means for delaying the application ofsaid second axial force by said second punch element until fulldensification of said hub portion is substantially completed.
 6. Theapparatus of claim 5 wherein said first punch element includes a tubularmember having an end face which substantially matches a terminal endface of the hub portion of said powder metal compact.
 7. The apparatusof claim 6 wherein said second punch element comprises a tubular elementpositioned concentrically around said first punch element and whereinsaid second punch element has an end face which defines a back face ofthe main body portion of the final product to be produced.
 8. Theapparatus of claim 5 wherein said core rod means is provided with aspline configuration on its outer surface so as to form a splineconfiguration along the bore of said compact as the compact is pressedinto position of said core rod means.
 9. The apparatus of claim 8wherein said first punch element includes a spline configuration on asurface which mates with the outer surface of said core rod means. 10.The apparatus of claim 7 wherein said first and second punch elementsare mounted in a common ram structure driven by said driving means sothat both of said punch elements are moved together toward said die witheach forming stroke of the ram structure, and wherein said second punchelement is resiliently mounted relative to said first punch element sothat said second punch element is delayed in its forward movement, uponengaging a portion of said compact, until said first punch element hasadvanced for a sufficient distance to substantially completely densifythe hub portion of the compact.
 11. The apparatus of claim 5 whereinsaid die cavity has a configuration which establishes gear toothprofiles on a compact densified therein.
 12. The apparatus of claim 5wherein said powder metal compact has a shape which allows fullinsertion of the compact into said die cavity by the action of saidfirst punch element and without a bending moment being applied to themain portion of the compact relative to its hub portion.